Why can't Rhino fillet this object?

Greetings fellow Rhinomaniacs,

Simple question: Why can’t Rhino fillet this object? All edges radius 10 mm
Fillet.3dm (262.1 KB)

gr, Tobias

Rhino’s FilletEdge doesn’t like that sharp edge. If you FilletSrf that one at 10.01, then trim off the excess and join, you can fillet the rest at 10.

Hi Mitch,
I know this kind of workarounds, but it’s lousy. Messing with the radius like this shouldn’t be necessary at all. .

We are in 2022, currently Rhino 7, with fancy SubD and what not, but this kind of basic fillet is failing? I don’t get it.

And it’s a basic fillet. I can easily do it by hand: Fillet 001.3dm (383.2 KB)

gr, Tobias


i dont see that as a typical basic fillet at all at. or is that something you produce constantly?
on the other side, Mac Rhino does not even fillet that after using Fillet Surface on that sharp edge. it still fails with blendedge and filletedge…

Dear @tobias

the edge in question is a 180 or 360-degree edge. Quite sure this will generate special cases, as for example the cross product will generate a 0 (vector).

solutions / workarrounds:

to get a fast solution
_offsetSrf -10 (to the inside)
_offsetSrf 10 with corner = round (to outside)

prepare the edge to allow filleting:
_extractSrf (the radial surface, copy = no)
_split (isocurve, shring=yes) a quite small part near the edge
_extendSrf (line, merge=yes)
_createSolid (or trim,join …)
→ filletEdge R10 works fine

see attached file

Fillet-2_tp.3dm (510.2 KB)


fwiw, sw 2017 has no issues with that

well - rhino does not have the most powerful fillet-algorithm - i agree on this.

also this exercise is much easier in sw than in rhino

Hi Tom, the simple fact that all this is necessary for a simple fillet is kinda embarrassing. Rhino should / must do this for me.

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It’s maybe not a “typical” fillet (if something like that exist) but its certainly a case Rhino should handle with ease.

Exactly Gijs! And Rhino shouldn’t either

Wicked! :sunglasses:

Although for me this threat was about bringing attention to this shortcoming of Rhino, I must say your solutions are pretty smart!


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Hmmm, I also have trouble with fillets sometimes, and while I can’t explain why Rhino fails at them so often…knowing that it does, I might recommend for shapes like this, filleting the corner of a surface first, then extruding the surface, then filleting all the other edges.

And I just tried that and DRATS, FOILED AGAIN!